I. Field of the Invention
This invention relates generally to stents for maintaining a passageway in an animal body patent, and more particularly to a stent specifically designed for use in treating chronic sinusitis where the sphenoid sinus is involved.
II. Discussion of the Prior Art
The paranasal sinuses are air-filled pockets located within the bones of the face and around the nasal cavity. Each sinus is named for the bone in which it is located, e.g., maxillary, ethmoid, frontal and sphenoid.
Each of these air-filled pockets has an opening that connects to the nose. This opening is called an ostium.
The nose and sinuses are closely related. The nasal septum divides the nose into two nasal cavities. The sidewall of the nose (the lateral nasal wall) has three important structures, which are known as the superior, middle and inferior turbinates sometimes referred to as nasal concha. Each is a rounded projection that extends the length of the nasal cavity. The space between each turbinate is called a meatus. Each meatus is named for the turbinate above it.
The inferior turbinate, which is larger than the other turbinates, runs parallel to the floor of the nose. The nasal nasolacrimal duct drains tears into the inferior meatus.
The middle turbinate is located above the inferior turbinate. The anterior or front ethmoid cells open into the middle meatus. The frontal sinus drains into the middle meatus.
The superior turbinate, which is the smallest turbinate, is above the middle turbinate. The posterior ethmoid cells drain into the superior meatus. The space between the superior turbinate, the septum and the sphenoid sinus front wall is known as the sphenoethmoid recess. The sphenoid sinus drains into this recess.
The paranasal sinuses are covered with a special lining or epithelium. The lining secretes mucous, a complex substance that keeps the nose and sinuses moist. The sinus epithelium is ciliated; that is, each cell on its surface has a cilium, which is a relatively long structure that has the capacity to push sinus mucous. This movement of mucous called mucociliary clearance is not random, but rather it is programmed so that the mucous moves along in a specific pattern.
The mucous membranes lining the nasal cavity and the paranasal sinuses may become inflamed due to infections, such as the common cold or allergies. When inflamed, the blood vessel dilates, the membranes swell and the mucous secretions increase. The resulting congestion interferes with breathing and often causes a “runny nose”. The infection may spread into the mucous membranes of the paranasal sinuses, blocking their connection with the nasal cavity and causing them to fill with mucous. Since the sinuses act as resonance chambers, this changes the sound of the voice and may also cause such a pressure increase within the sinuses that severe headaches result.
Chronic sinusitis is arbitrary defined as rhinosinusitis of at least 12 consecutive weeks duration and persistence of one major and two minor signs and/or symptoms. Major signs and symptoms include fever, facial pain or pressure, nasal obstruction or nasal discharge with purulence and hyposmia. Cough, dental pain, headache and ear pain or ear fullness are considered minor signs and symptoms. The sphenoid sinus normally drains through its ostium into the space between the superior and middle turbinates. However, due to infection or possibly other causes, the membranes proximate the ostium may swell to the point where drainage ceases and fluid pressure builds up creating severe pain behind the eyes. In treating chronic sphenoid sinusitis, under endoscopic guidance, the ostium of the sphenoid sinus is surgically enlarged to facilitate drainage from the sphenoid sinus cavity. However, tissue swelling and surgical exudates at the surgical site may narrow or scar tissue may close the ostium. Thus a need exists for a means whereby the surgically created opening will remain patent for a period of time sufficient to treat the sinusitis condition.